Looking Up: Watching for a new star’

Peter Becker

Friday

Jun 24, 2011 at 12:01 AMJun 24, 2011 at 1:19 PM

Imagine seeing a star where none was noticed before. You would probably make a really big wish and hope it was still there when you looked again. Diligent observers with even relatively small backyard telescopes have been enjoying a supernova during June, which erupted in the famed Whirlpool Galaxy, M51.

Imagine seeing a star where none was noticed before. You would probably make a really big wish and hope it was still there when you looked again.

Diligent observers with even relatively small backyard telescopes have been enjoying a supernova during June, which erupted in the famed Whirlpool Galaxy, M51.

One of these nights we are bound to look up and not even need a telescope to see a “new star” among the thousands sprinkled across the sky. An exploding star, which we know a a supernova, briefly outshines any star in the entire galaxy in which it is a part.

We have not witnessed a supernova in the Milky Way Galaxy in several hundred years, but they are occasionally noticed by telescopic observers in other galaxies.

In the early 1990s I had the chance to see a supernova in the Whirlpool Galaxy, as well as another in a second galaxy, M81. It looked like a very dim star superimposed on the faint haze of the galaxy.

This is certainly not going to excite a large amount of the general public. Yet imagine that this faint star is visible at all, exploding in a galaxy many millions of light years away. In your telescope, a distant galaxy appears as a faint, fuzzy spot; other than the wonder of a supernova rising to prominence, you won’t see the true nature of that dim haze, which is really billions of individual stars intermingled with nebulous clouds of gas and dust, like our own home galaxy.

The abundance of dusty nebulosity filling our own Milky Way likely have hidden the light of supernovae in farther reaches of the galaxy, from our eyes.

Surveillance by X-ray detectors in space and radio observatories on Earth would be expected to pick up signs of a Milky Way supernova. X-rays and radio waves, however, are not visible to the eye.

Supernovae have startled the public in centuries past. These include a brilliant “new star” in the constellation Ophiuchus in 1604 and another in Cassiopeia in 1572, and in Taurus the Bull in 1054. At their heights, these supernovae rivaled the brilliant planet Venus in magnitude.

Once a supernova suddenly flares into view, the light gradually diminishes over the next few months. Remnants of long ago supernovae can be viewed as expanding shells of gas and dust. A 6-inch telescope can easily show a few of these, as faint, nebulous wisps or spots.

Based on the number of supernovae seen in other galaxies, astronomers estimate about three explode every century in the Milky Way.

The most recent supernova in our galaxy was detected in 2008 by NASA's Chandra X-ray Observatory and the National Radio Astronomy Observatory's Very Large Array.

The supernova explosion occurred about 140 years ago, making it the most recent in the Milky Way. Its light, however, was hidden by the thick dust and gas of the Milky Way’s core.

Due to the shock wave sent out by a supernova, any occurring within about 50 to 100 light years away would likely destroy life on Earth, astronomers say. The sort of the most commonly observed supernova, the “Type II” is a massive star that suddenly collapses on itself. Astronomers reassure that there are no massive stars capable of an explosion, close enough to cause concern.

Another cosmic event is the nova, a cataclysmic eruption caused by hydrogen being drawn from a star into a dense white dwarf star in a tight double star system. At very rare times a nova will appear to the naked eye in the sky as a temporary “new star.” In 1975, a nova erupted to +2nd magnitude, temporarily altering the appearance of the constellation Cygnus the Swan. This is similar to the brightness of most of the Big Dipper’s stars.

About 10 novae are discovered in the Milky Way each year.

New moon is on July 1.

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